Nadine Goeppert

Colloid Transport with Wetting Fronts: Interactive Effects of Solution Surface Tension and Ionic Strength

Transport of colloids with transient wetting fronts represents an important mechanism of contaminant migration in the vadose zone. The work presented here used steady-state saturated and transient unsaturated flow columns to evaluate the transport of a fluorescent latex microsphere (980 nm in diameter) with capillary wetting fronts of different solution surface tensions and ionic strengths. The saturated transport experiments demonstrated that decreasing solution surface tension and ionic strength decreased colloid deposition at the solid-liquid interface and increased colloid recovery in the column effluent. The effect of solution surface tension on colloid transport and deposition was greater at lower ionic strength, suggesting an interaction between these two factors. Under transient unsaturated flow conditions, the number of colloids retained in sand decreased exponentially with travel distance through the porous media. However, lowering the solution surface tension and ionic strength resulted in a more even distribution of colloids along the column. The measured zeta potentials of colloids in different solutions suggest that both lowering surface tension and ionic strength would enhance the electrostatic repulsion between colloid and sand. The experimental results revealed that the effects are nonlinear, implying the possible existence of critical threshold values, beyond which the effects were not significant. In addition, colloid migration slowed down as solution surface tension decreased due to reduction of capillary forces that drove liquid movement.

Detection, fate and transport of estrogen family hormones in soil

Estrone (E1), 17β-estradiol (E2), and estrone-sulfate (E1-3S) are released into the environment in significant amounts. They are known to adversely affect the endocrine systems of aquatic organisms. Although previous studies clearly demonstrate that free hormones sorb strongly to soil and degrade quickly, significant amounts of free and the more persistent conjugated estrogens can be still detected in various environmental media. To date, E1-3S has been considered as a metabolite that forms either during the animal hormone cycle or as a degradation product of precursor hormones like E2-3S. We performed small-scale laboratory column tests to investigate two major features: transport and degradation of E2, and formation of E1-3S and E1. To evaluate the influence of soil microbial activity, one portion of soil was autoclaved and the background solution treated with sodium azide. The results demonstrate that (i) E2 is degraded to E1 and E1-3S in non-autoclaved soil, and to E1 in autoclaved soil, (ii) the formation of E1-3S is biologically driven, and (iii) the transformation of E2 to E1 does not require biological interaction. An inverse modeling approach was used to quantify the transport parameters and degradation rate coefficients.

Transport and variability of fecal bacteria in carbonate conglomerate aquifers.

Clastic sedimentary rocks are generally considered non-karstifiable and thus less vulnerable to pathogen contamination than karst aquifers. However, dissolution phenomena have been observed in clastic carbonate conglomerates of the Subalpine Molasse zone of the northern Alps and other regions of Europe, indicating karstification and high vulnerability, which is currently not considered for source protection zoning. Therefore, a research program was established at the Hochgrat site (Austria/Germany), as a demonstration that karst-like characteristics, flow behavior, and high vulnerability to microbial contamination are possible in this type of aquifer. The study included geomorphologic mapping, comparative multi-tracer tests with fluorescent dyes and bacteria-sized fluorescent microspheres, and analyses of fecal indicator bacteria (FIB) in spring waters during different seasons. Results demonstrate that (1) flow velocities in carbonate conglomerates are similar as in typical karst aquifers, often exceeding 100 m/h; (2) microbial contaminants are rapidly transported toward springs; and (3) the magnitude and seasonal pattern of FIB variability depends on the land use in the spring catchment and its altitude. Different groundwater protection strategies that currently applied are consequently required in regions formed by karstified carbonatic clastic rocks, taking into account their high degree of heterogeneity and vulnerability.

Erratum: Impact of managed aquifer recharge on the chemical and isotopic composition of a karst aquifer, Wala reservoir, Jordan

Storm-water harvesting and storage via managed aquifer recharge (MAR) is a promising approach to combat water scarcity in semi-arid regions, but poses a challenge for karst aquifers and regions with highly variable water availability. The infiltration of low-mineralized surface water and its impact on highly mineralized groundwater of a karst aquifer was investigated at Wala reservoir in Jordan over a period of approximately 10 years. The results show significant groundwater-level rise in a wellfield, in response to the yearly average infiltration of about 6.7 million m3. This corresponds to about 60 % of the yearly average abstraction of about 11.7 million m3, confirmed by mixing calculations with tritium. A decreasing trend in infiltration due to sedimentation is observed. Mean groundwater residence times of several thousand years, derived from carbon-14 dating, indicate a large storage capacity of the aquifer. The heterogeneous distribution of the residence times is caused by strong groundwater withdrawals and artificial recharge along with karst-specific aquifer characteristics. Temporal groundwater salinity fluctuations in the wellfield are observed after the first MAR infiltration. Enhanced groundwater flow along the wadi course was demonstrated, which is an important aspect with regards to future MAR projects in similar wadis of the region.

Fate and transport of free and conjugated estrogens during soil passage

Endocrine disrupting chemicals, such as the free estrogens 17β-estradiol (E2), estrone (E1) and the conjugated estrogen estrone-sulfate (E1-3S) are found at low concentration levels in the environment. This is somehow contradictory to the strong sorption and high degradation potentials found in laboratory experiments. In particular, the fate and transport behavior of conjugated estrogens is poorly understood, and the importance of enzymes triggering the transformation pathways has received little attention. To address these deficiencies, the present research uses packed laboratory soil columns with pulse injections of free estrogens, either E2 or E1, or E1-3S, to provide sound evidence of the transformation pathways. It is further shown that (i) transport of free estrogens is subject to strong retardation and degradation, (ii) the transport of conjugated estrogens is less retarded and only to a minor degree affected by degradation, and (iii) arylsulfotransferase is the enzyme triggering the transformation reaction.

Evaluation of β-d-glucuronidase and particle-size distribution for microbiological water quality monitoring in Northern Vietnam.

In many karst regions in developing countries, the populations often suffer from poor microbial water quality and are frequently exposed to bacterial pathogens. The high variability of water quality requires rapid assays, but the conventional cultivation-based analysis of fecal indicator bacteria, such as Escherichia coli (E. coli), is very time-consuming. In this respect, the measurement of the enzymatic activity of E. coli could prove to be a valuable tool for water quality monitoring. A mobile automated prototype device was used for the investigation of β-d-glucuronidase (GLUC) activity at a remote karst spring, connected to a sinking surface stream, in Northern Vietnam. To assess the relationship between GLUC activity, discharge dynamics and contamination patterns, multiple hydrological, hydrochemical, physicochemical and microbiological parameters, including discharge, turbidity, particle-size distributions, and E. coli, were measured with high temporal resolution during ten days of on-site monitoring. A complex contamination pattern due to anthropogenic and agricultural activities led to high E. coli concentrations (270 to >24,200 MPN/100ml) and a GLUC activity between 3.1 and 102.2 mMFU/100ml. A strong daily fluctuation pattern of GLUC activity and particle concentrations within small size classes (<10μm) could be observed, as demonstrated by autocorrelations. A Spearmans rank correlation analysis resulted in correlation coefficients of rs=0.56 for E. coli and GLUC activity and rs=0.54 for GLUC activity and the concentration of 2-3μm particles. On an event scale, correlations were found to be higher (rs=0.69 and 0.87, respectively). GLUC activity and E. coli displayed a general contamination pattern, but with significant differences in detail, which may be explained by interferences of e. g. viable but non-culturable cells. Although further evaluations are recommended, GLUC activity is a promising, complementary parameter for on-site and near real-time water quality monitoring.

Isotopic constraints on water source mixing, network leakage and contamination in an urban groundwater system

Water supply in developing countries is prone to large water losses due to leaky distribution networks and defective sewers, which may affect groundwater quality and quantity in urban areas and result in complex subsurface mixing dynamics. In this study, a multi-stable isotope approach was used to investigate spatiotemporal fluctuations of surface and sub-surface water source partitioning and mixing, and to assess nitrogen (N) contamination in the urban water cycle of As-Salt, Jordan. Water import from the King Abdullah Canal (KAC), mains waters from the network, and wastewater are characterized by distinct isotopic signatures, which allowed us to quantify city effluents into the groundwater. Temporal variations in isotopic signatures of polluted groundwater are explained by seasonally fluctuating inflow, and dilution by water that originates from Lake Tiberias and enters the urban water cycle via the KAC. Isotopic analysis (N and O) and comparison between groundwater nitrate and nitrate from mains water, water imports and wastewater confirmed that septic waste from leaky sewers is the main contributor of nitrate contamination. The nitrate of strongly contaminated groundwater was characterized by highest δ15NNO3 values (13.3±1.8‰), whereas lowest δ15NNO3 values were measured in unpolluted groundwater (6.9‰). Analogously, nitrate concentration and isotopic ratios were used for source partitioning and qualitatively confirmed δDH2O and δ18OH2O-based estimates. Dual water isotope endmember mixing calculations suggest that city effluents from leaky networks and sewers contribute 30-64% to the heavily polluted groundwater. Ternary mixing calculations including also chloride revealed that 5-18% of the polluted groundwater is wastewater. Up to two thirds of the groundwater originates from mains, indicating excessive water loss from the network, and calling for improved water supply management.

Fluorescence-based multi-parameter approach to characterize dynamics of organic carbon, faecal bacteria and particles at alpine karst springs

Karst springs, especially in alpine regions, are important for drinking water supply but also vulnerable to contamination, especially after rainfall events. This high variability of water quality requires rapid quantification of contamination parameters. Here, we used a fluorescence-based multi-parameter approach to characterize the dynamics of organic carbon, faecal bacteria, and particles at three alpine karst springs. We used excitation emission matrices (EEMs) to identify fluorescent dissolved organic material (FDOM). At the first system, peak A fluorescence and total organic carbon (TOC) were strongly correlated (Spearmans rs of 0.949), indicating that a large part of the organic matter is related to humic-like substances. Protein-like fluorescence and cultivation-based determination of coliform bacteria also had a significant correlation with rs=0.734, indicating that protein-like fluorescence is directly related to faecal pollution. At the second system, which has two spring outlets, the absolute values of all measured water-quality parameters were lower; there was a significant correlation between TOC and humic-like fluorescence (rs=0.588-0.689) but coliform bacteria and protein-like fluorescence at these two springs were not correlated. Additionally, there was a strong correlation (rs=0.571-0.647) between small particle fractions (1.0 and 2.0μm), a secondary turbidity peak and bacteria. At one of these springs, discharge was constant despite the reaction of all other parameters to the rainfall event. Our results demonstrated that i) all three springs showed fast and marked responses of all investigated water-quality parameters after rain events; ii) a constant discharge does not necessarily mean constant water quality; iii) at high contamination levels, protein-like fluorescence is a good indicator of bacterial contamination, while at low contamination levels no correlation between protein-like fluorescence and bacterial values was detected; and iv) a combination of fluorescence measurements and particle-size analysis is a promising approach for a rapid assessment of organic contamination, especially relative to time-consuming conventional bacterial determination methods.

Contamination risk and drinking water protection for a large-scale managed aquifer recharge site in a semi-arid karst region, Jordan

Karst aquifers in semi-arid regions are particularly threatened by surface contamination, especially during winter seasons when extremely variable rainfall of high intensities prevails. An additional challenge is posed when managed recharge of storm water is applied, since karst aquifers display a high spatial variability of hydraulic properties. In these cases, adapted protection concepts are required to address the interaction of surface water and groundwater. In this study a combined protection approach for the surface catchment of the managed aquifer recharge site at the Wala reservoir in Jordan and the downstream Hidan wellfield, which are both subject to frequent bacteriological contamination, is developed. The variability of groundwater quality was evaluated by correlating contamination events to rainfall, and to recharge from the reservoir. Both trigger increased wadi flow downstream of the reservoir by surface runoff generation and groundwater seepage, respectively. A tracer test verified the major pathway of the surface flow into the underground by infiltrating from pools along Wadi Wala. An intrinsic karst vulnerability and risk map was adapted to the regional characteristics and developed to account for the catchment separation by the Wala Dam and the interaction of surface water and groundwater. Implementation of the proposed protection zones for the wellfield and the reservoir is highly recommended, since the results suggest an extreme contamination risk resulting from livestock farming, arable agriculture and human occupation along the wadi. The applied methods can be transferred to other managed aquifer recharge sites in similar karstic environments of semi-arid regions.ZusammenfassungKarstgrundwasserleiter in semiariden Gebieten sind im besonderen Maße von Oberflächenverschmutzung bedroht, vor allem während der Wintersaison, wenn extrem variabler Niederschlag von hoher Intensität vorherrscht. Eine zusätzliche Herausforderung stellt die künstliche Grundwasseranreicherung mit Niederschlagswasser dar, da Karstgrundwasserleiter eine hohe räumliche Variabilität in ihren hydraulischen Eigenschaften aufweisen. In diesen Fällen sind angepasste Schutzkonzepte erforderlich, die das Zusammenspiel von Oberflächenwasser und Grundwasser berücksichtigen. In dieser Studie wird ein kombiniertes Schutzkonzept für das Oberflächeneinzugsgebiet der künstlichen Grundwasseranreicherungsanlage am Wala Stausee und dem unterstromig gelegenen Hidan Brunnenfeld in Jordanien entwickelt. In Beiden wurden wiederholt bakteriologische Verunreinigungen festgestellt. Die Variabilität der Grundwasserqualität lässt sich durch Korrelation der Kontaminationsereignisse mit Niederschlagsereignissen und Infiltration aus dem Stausee erklären. Beides führt zu erhöhtem Abfluss im Wadi unterhalb des Stausees, hervorgerufen durch Oberflächenabfluss und Grundwasseraustritte. Ein Tracerversuch bestätigte die Infiltration des Oberflächenflusses in den Untergrund über Pools entlang des Wadi Wala. Eine intrinsische Karstvulnerabilitäts- und Risikokarte wurde entwickelt und an die regionalen Besonderheiten angepasst, um die Abtrennung des Einzugsgebiets durch den Wala Staudamm und das Zusammenwirken von Oberflächenwasser und Grundwasser zu berücksichtigen. Die Umsetzung der vorgeschlagenen Schutzzonen für das Brunnenfeld und das Reservoir wird dringend empfohlen, da die Ergebnisse ein extremes Kontaminationsrisiko durch Viehzucht, Ackerbau und menschliche Besiedlung entlang des Wadis zeigen. Die angewandten Methoden können auf andere künstliche Grundwasseranreicherungsanlagen in ähnlichen Karstgebieten semiarider Regionen übertragen werden.RésuméLes aquifères karstiques dans les régions semi-arides sont particulièrement menacés par une contamination provenant de la surface, surtout pendant les saisons hivernales où prévaut une pluviométrie extrêmement variable de fortes intensités. Un défi supplémentaire existe lorsque la gestion de la recharge par les eaux pluviales est. appliquée, car les aquifères karstiques présentent une grande variabilité spatiale des propriétés hydrauliques. Dans ces cas, des concepts de protection adaptée sont nécessaires pour traiter la question des interactions entre les eaux de surface et les eaux souterraines. Dans cette étude, une approche combinée de protection est. développée pour le bassin versant du site de recharge de l’aquifère au niveau du réservoir de Wala en Jordanie et du champ de captage d’Hidan situé en aval hydraulique, tous les deux sujets à une contamination bactériologique fréquente. La variabilité de la qualité des eaux souterraines a été évaluée en corrélant les événements de contamination avec les précipitations, et à la recharge à partir du réservoir. Les deux déclenchent une augmentation du débit de l’oued en aval du réservoir due à la génération d’un ruissellement de surface et à l’infiltration vers les eaux souterraines, respectivement. Un essai de traçage a vérifié la voie principale de l’écoulement de surface dans le sous-sol par infiltration à partir des bassins situés le long de l’oued Wala. Une carte de la vulnérabilité intrinsèque du karst et de risque a été adaptée aux caractéristiques régionales et élaborée pour prendre en considération la séparation des bassins versants par le barrage de Wala et l’interaction entre les eaux de surface et les eaux souterraines. La mise en œuvre des zones de protection proposées pour le champ de captage et le réservoir est. fortement recommandée, car les résultats suggèrent un risque de contamination extrême résultant de l’élevage, de l’agriculture et des habitations le long de l’oued. Les méthodes appliquées peuvent être transférées à d’autres sites de recharge des aquifères dans des environnements karstiques similaires en régions semi-arides.ResumenLos acuíferos kársticos de las regiones semiáridas están particularmente amenazados por la contaminación desde la superficie, especialmente durante las estaciones invernales cuando prevalecen lluvias extremadamente variables de altas intensidades. Un desafío adicional se plantea cuando se aplica gestión de la recarga de aguas pluviales, ya que los acuíferos kársticos muestran una alta variabilidad espacial de sus propiedades hidráulicas. En estos casos, se requieren conceptos de protección adaptados para abordar la interacción entre el agua superficial y subterránea. En este estudio se desarrolla un enfoque combinado de protección para la cuenca superficial de un sitio de recarga del acuífero gestionado en el embalse de Wala en Jordania y el campo de pozos Hidan aguas abajo, ambos sujetos a una frecuente contaminación bacteriológica. La variabilidad de la calidad del agua subterránea se evaluó mediante la correlación de los eventos de contaminación con las precipitaciones y la recarga desde el embalse. Ambos desencadenan el aumento del flujo del wadi, río abajo del reservorio por la generación de escorrentía de superficie y filtración de agua subterránea, respectivamente. Una prueba de trazadores verificó la trayectoria principal del flujo superficial en el subsuelo por infiltración a partir de estanques a lo largo de Wadi Wala. Se adaptó un mapa de vulnerabilidad intrínseca y de riesgo kárstico a las características regionales y se desarrolló para tener en cuenta la separación de las cuencas por la presa de Wala y la interacción del agua superficial y subterránea. La implementación de las zonas de protección propuestas para el pozo y el embalse es altamente recomendable, ya que los resultados sugieren un riesgo extremo de contaminación como resultado de la ganadería, la agricultura y la ocupación humana a lo largo del wadi. Los métodos aplicados pueden ser transferidos a otros sitios gestionados de recarga de acuíferos en ambientes kársticos similares de regiones semiáridas.摘要半干旱地区的岩溶含水层特别容易受到地表污染的威胁,尤其是在极度变化的高强度降雨盛行的冬季。在应用雨水作为补给的时候还有额外的挑战,因为岩溶含水层的水文特性空间变化很大。在这些情况下,需要适合的保护概念来强调地表水和地下水的相互作用。在本研究中,对约旦Wala储水地区管理的含水层补给地地表流域及下游的Hidan井场提出了一项组合保护方法,这两个区域常常受到微生物的污染。通过污染事件与降雨以及污染与储水地补给的对比,评价了水质的变化性。两者分别通过产生地表径流和地下水渗漏导致旱谷流向下游的水流增加。示踪实验证实了地表水流从沿Wala旱谷的池塘入渗进入地下的主要通道。针对区域特征对固有的岩溶脆弱性和风险图进行了改编并改进,来说明Wala大坝的流域划分和地表水与地下水的相互作用。强烈建议在井场和储水地建立提出的保护帶,因为研究结果表明,沿旱谷的畜牧耕作、耕地农业和人类侵占致使污染风险极高。这个实用方法可应用在半干旱区域类似岩溶环境种其它管理的含水层补给场地。.ResumoAquíferos cársticos em regiões semiáridas são particularmente ameaçados por contaminação superficial, especialmente durante as estações de inverno quando prevalecem precipitações extremamente variáveis e de alta intensidade. Um desafio adicional é criado quando o gerenciamento de recarga da água da chuva é aplicado, já que os aquíferos cársticos apresentam uma alta variabilidade espacial de propriedades hidráulicas. Nestes casos, são necessários conceitos de proteção adaptados para abordar a interação entre águas superficiais e subterrâneas. Nesse estudo, desenvolveu-se uma abordagem de proteção combinada para a captação superficial na área de gerenciamento de recarga no reservatório Wala, na Jordânia, e no campo de poços Hidan, a jusante, ambos sujeitos à frequente contaminação bacteriológica. A variabilidade da qualidade das águas subterrâneas foi avaliada correlacionando os eventos de contaminação com a precipitação e recarga do reservatório. Ambos desencadeiam o aumento do fluxo do Wadi a jusante do reservatório pela geração do escoamento superficial e infiltração das águas subterrâneas, respectivamente. Um teste de traçadores verificou o caminho principal do fluxo superficial para o subsolo por infiltração de lagoas ao longo do Wadi Wala. Um mapa de vulnerabilidade intrínseca e risco do cárste foi adaptado às características regionais e desenvolvido para explicar a separação da bacia hidrográfica pela barragem de Wala e a interação entre águas superficiais e subterrâneas. A implementação das zonas de proteção propostas para o campo de poços e o reservatório é altamente recomendado, já que os resultados sugerem um risco extremo de contaminação resultante da pecuária, agricultura e ocupação humana ao

Hydrogeological controls of variable microbial water quality in a complex subtropical karst system in Northern Vietnam

Karst aquifers are particularly vulnerable to bacterial contamination. Especially in developing countries, poor microbial water quality poses a threat to human health. In order to develop effective groundwater protection strategies, a profound understanding of the hydrogeological setting is crucial. The goal of this study was to elucidate the relationships between high spatio-temporal variability in microbial contamination and the hydrogeological conditions. Based on extensive field studies, including mapping, tracer tests and hydrochemical analyses, a conceptual hydrogeological model was developed for a remote and geologically complex karst area in Northern Vietnam called Dong Van. Four different physicochemical water types were identified; the most important ones correspond to the karstified Bac Son and the fractured Na Quan aquifer. Alongside comprehensive investigation of the local hydrogeology, water quality was evaluated by analysis for three types of fecal indicator bacteria (FIB): Escherichia coli, enterococci and thermotolerant coliforms. The major findings are: (1) Springs from the Bac Son formation displayed the highest microbial contamination, while (2) springs that are involved in a polje series with connections to sinking streams were distinctly more contaminated than springs with a catchment area characterized by a more diffuse infiltration. (3) FIB concentrations are dependent on the season, with higher values under wet season conditions. Furthermore, (4) the type of spring capture also affects the water quality. Nevertheless, all studied springs were faecally impacted, along with several shallow wells within the confined karst aquifer. Based on these findings, effective protection strategies can be developed to improve groundwater quality.RésuméLes aquifères karstiques sont particulièrement vulnérables à la contamination bactérienne. La mauvaise qualité de l’eau du point de vue microbien constitue une menace pour la santé humaine, en particulier dans les pays en développement. Afin de développer des stratégies efficaces de protection des eaux souterraines, une compréhension détaillée du contexte hydrogéologique est cruciale. L’objectif de cette étude était de comprendre les relations entre la variabilité élevée spatio-temporelle de la contamination microbienne et les conditions hydrogéologiques. A partir de vastes études de terrain, comprenant de la cartographie, des essais de traçage et des analyses hydrochimiques, un modèle hydrogéologique conceptuel a été développé pour une zone karstique éloignée et géologiquement complexe, appelée Dong Van et située au Nord du Vietnam. Quatre différents types d’eau physicochimiques ont été identifiés; le plus important correspond à l’aquifère karstifié Bac Son et à l’aquifère fracturé Na Quan. Parallèlement à l’étude approfondie de l’hydrogéologie à l’échelle locale, la qualité de l’eau a été évaluée à partir de l’analyze de trois types de bactéries indicatrices d’origine fécale (BIF): Escherichia coli, entérocoques et coliformes thermotolérants. Les principaux résultats sont: (1) les sources de la formation de Bac Son sont caractérisées par la contamination microbienne la plus élevée, alors que (2) les sources qui sont associées à des séries de poljes connectés des cours d’eau avec des pertes sont de manière distincte plus contaminées que les sources dont le bassin d’alimentation est. caractérisé par une infiltration plus diffuse. (3) Les concentrations en BIF varient en fonction de la saison, avec les plus fortes valeurs lors des conditions de saison humide. De plus, (4) le type de captage des sources impacte également la qualité de l’eau. Néanmoins, toutes les sources étudiées sont impactées par une contamination d’origine fécale, ainsi que plusieurs puits peu profonds dans l’aquifère karstique captif. Sur la base de ces résultats, des stratégies de protection efficace peuvent être développées pour améliorer la qualité des eaux souterraines.ResumenLos acuíferos kársticos son particularmente vulnerables a la contaminación bacteriana. Especialmente en los países en desarrollo, la mala calidad microbiana del agua plantea una amenaza para la salud humana. Para desarrollar estrategias efectivas de protección del agua subterránea es crucial una comprensión profunda del ambiente hidrogeológico. El objetivo de este estudio fue dilucidar las relaciones entre la alta variabilidad espacio-temporal de la contaminación microbiana y las condiciones hidrogeológicas. Con base en extensos estudios de campo, que incluyen mapeo, pruebas de trazadores y análisis hidroquímicos, se desarrolló un modelo hidrogeológico conceptual para una lejana y geológicamente compleja área kárstica en el norte de Vietnam llamada Dong Van. Se identificaron cuatro tipos fisicoquímicos diferentes de aguas; los más importantes corresponden al Bac Son karstificado y al acuífero fracturado de Na Quan. Junto a la investigación exhaustiva de la hidrogeología local, la calidad del agua se evaluó mediante el análisis de tres tipos de bacterias fecales indicadoras (FIB): Escherichia coli, enterococos y coliformes termotolerantes. Los principales hallazgos son: (1) los manantiales de la formación Bac Son mostraron la contaminación microbiana más alta, mientras que (2) los manantiales que están involucrados en una serie de poljés con conexiones a corrientes de hundimiento estaban claramente más contaminados que los manantiales con un área de captación caracterizada por infiltración más difusa (3) las concentraciones de FIB dependen de la temporada, con valores más altos en condiciones de estación lluviosa. Además, (4) el tipo de captura de manantiales también afecta la calidad del agua. Sin embargo, todos los manantiales estudiados fueron impactados fecalmente, junto con varios pozos poco profundos dentro del acuífero kárstico confinado. Con base en estos hallazgos, se pueden desarrollar estrategias efectivas de protección para mejorar la calidad del agua subterránea.摘要岩溶系统特别容易受到细菌污染。特别是在发展中国家,很差的微生物水质给人类健康带来威胁。为了实施有效的地下水保护策略,对水文地质背景渗入了解至关重要。本研究的目的就是弄清微生物污染很高的时空多变性与水为之条件之间的相互关系。在广泛室外研究的基础上,包括填图、示踪试验和水化学分析,针对越南北部一个偏远和地质上非常复杂的岩溶区(被称为Dong Van的地方)建立了水文地质概念模型。确定了四种不同的物理化学水类型;最重要的水类型与岩溶化的Bac Son含水层和断裂的Na Quan含水层一致。除了对当地进行了综合水文地质调查,还通过对三种排泄物指示细菌----大肠杆菌、肠球菌和耐热大肠杆菌进行了评估。主要发现是:(1)Bac Son地层的泉水显示微生物污染程度最高,(2)而灰岩盆地与落渗河相关联的泉水比弥散入渗强度更高的汇水区的泉水受到的污染更明显;(3)排泄物指示细菌含量取决于季节,雨季条件下含量值较高。此外,(4)泉水的来源也影响着水质。然而,所有研究的泉与承压岩溶含水层的几口浅层井一起,都受到排泄物的影响。基于这些发现,可提出有效的保护策略以改善地下水水质。ResumoAquíferos cársticos são particularmente vulneráveis à contaminação bacteriana. Especialmente nos países em desenvolvimento, a má qualidade microbiana da água representa uma ameaça para a saúde humana. A fim de desenvolver estratégias eficazes de proteção das águas subterrâneas, é crucial uma compreensão mais profunda do cenário hidrogeológico. O objetivo deste estudo foi elucidar as relações entre a alta variabilidade espaço-temporal na contaminação microbiana e as condições hidrogeológicas. Com base em extensos estudos de campo, incluindo mapeamento, testes com traçadores e análises hidroquímicas, foi desenvolvido um modelo hidrogeológico conceitual para uma área cárstica remota e geologicamente complexa no norte do Vietnã, chamada Dong Van. Foram identificados quatro diferentes tipos físico-químicos de águas; os mais importantes correspondem ao carstificado Bac Son e ao aquífero fraturado Na Quan. Juntamente com a abrangente investigação da hidrogeologia local, foi avaliada a qualidade da água via análise de três tipos de bactérias fecais indicadoras (BFI): Escherichia coli, enterococcus e coliformes termotolerantes. As principais conclusões são: (1) as nascentes da formação Bac Son apresentaram a maior contaminação microbiana, enquanto (2) as nascentes envolvidas em uma série de poljes com conexões a correntes de sumidouros foram nitidamente mais contaminadas do que nascentes com uma área de captação caracterizada por infiltração mais difusa. (3) As concentrações de BFI são dependentes da estação, com valores mais altos sob condições de estação chuvosa. Além disso, (4) o tipo de captura de nascente também afeta a qualidade da água. No entanto, todas as nascentes estudadas foram impactadas, juntamente com vários poços rasos dentro do aquífero cárstico confinado. Com base nesses resultados, estratégias eficazes de proteção podem ser desenvolvidas para melhorar a qualidade das águas subterrâneas.